U.S. patent application number 14/011887 was filed with the patent office on 2014-03-06 for silicon-containing dopant compositions, systems and methods of use thereof for improving ion beam current and performance during silicon ion implantation.
The applicant listed for this patent is Lloyd Anthony Brown, Serge Marius Campeau, Ashwini K. Sinha. Invention is credited to Lloyd Anthony Brown, Serge Marius Campeau, Ashwini K. Sinha.
Application Number | 20140061501 14/011887 |
Document ID | / |
Family ID | 49182494 |
Filed Date | 2014-03-06 |
United States Patent
Application |
20140061501 |
Kind Code |
A1 |
Sinha; Ashwini K. ; et
al. |
March 6, 2014 |
SILICON-CONTAINING DOPANT COMPOSITIONS, SYSTEMS AND METHODS OF USE
THEREOF FOR IMPROVING ION BEAM CURRENT AND PERFORMANCE DURING
SILICON ION IMPLANTATION
Abstract
A novel composition, system and method thereof for improving
beam current during silicon ion implantation are provided. The
silicon ion implant process involves utilizing a first
silicon-based co-species and a second species. The second species
is selected to have an ionization cross-section higher than that of
the first silicon-based species at an operating arc voltage of an
ion source utilized during generation and implantation of active
silicon ions species. The active silicon ions produce an improved
beam current characterized by maintaining or increasing the beam
current level without incurring degradation of the ion source when
compared to a beam current generated solely from SiF4.
Inventors: |
Sinha; Ashwini K.; (East
Amherst, NY) ; Brown; Lloyd Anthony; (East Amherst,
NY) ; Campeau; Serge Marius; (Lancaster, NY) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Sinha; Ashwini K.
Brown; Lloyd Anthony
Campeau; Serge Marius |
East Amherst
East Amherst
Lancaster |
NY
NY
NY |
US
US
US |
|
|
Family ID: |
49182494 |
Appl. No.: |
14/011887 |
Filed: |
August 28, 2013 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
61693916 |
Aug 28, 2012 |
|
|
|
Current U.S.
Class: |
250/424 ;
250/423R; 252/372 |
Current CPC
Class: |
H01J 37/08 20130101;
H01J 2237/006 20130101; H01J 37/3171 20130101 |
Class at
Publication: |
250/424 ;
250/423.R; 252/372 |
International
Class: |
H01J 37/08 20060101
H01J037/08 |
Claims
1. A dopant gas composition comprising: a silicon-based dopant gas
composition comprising a first silicon-based species and a second
species, wherein said second species is selected to have a
ionization cross-section higher than that of the first
silicon-based species at an operating arc voltage of an ion source
utilized during generation and implantation of active silicon ions;
wherein said silicon-based dopant gas composition improves the ion
beam current so as to maintain or increase beam current without
degradation of said ion source in comparison to a beam current
generated from silicon tetrafluoride (SiF4).
2. The dopant gas composition of claim 1, wherein said first
silicon-based species is selected from the group consisting of
SiH2Cl2, Si2H6, SiH4 SiF2H2, SiF4 and any combination thereof.
3. The dopant composition of claim 1, wherein said first
silicon-based species is SiF4.
4. The dopant composition of claim 1, wherein said first
silicon-based species is SiF4 and the second species is disilane
(S2H6).
5. The dopant composition of claim 4, wherein said S2H6 has a
concentration of less than 50% based on the overall volume of said
composition.
6. The dopant composition of claim 5, wherein said S2H6 has a
concentration of about 10% or less.
7. A system for providing an improved beam current during silicon
ion implantation, comprising: an ion source apparatus partially
defined by an arc chamber wall, wherein the chamber comprises a
silicon ion source disposed at least partially within the chamber
wall; one or more supply vessels in fluid communication with said
ion source apparatus, said vessels storing a silicon-based dopant
gas composition, said composition comprising a first silicon-based
species and a second species, wherein said second species is
selected to have an ionization cross-section higher than that of
the first silicon-based species at an operating arc voltage of the
ion source during implantation of active silicon ions; one or more
supply feed lines corresponding to the one or more supply vessels,
said feed lines extending from the one or more supply vessels
through the wall into the chamber; wherein said one or more vessels
are configured to dispense said silicon-based dopant composition
through said supply feed lines and into said ion source apparatus
thereby allowing the silicon ion source to ionize the silicon-based
dopant gas composition to generate at least a portion of the active
silicon ions from at least said first silicon-based species, the
active silicon ions producing an increased beam current in
comparison to a beam current generated solely from SiF4.
8. The system of claim 7, wherein said first silicon-based species
is selected from the group consisting of SiH2Cl2, Si2H6, SiH4
SiF2H2, SiF4 and any combination thereof.
9. The system of claim 7 wherein said first silicon-based species
is SiF4 and said second species is a silicon-based species, said
silicon-based species comprising Si2H6.
10. The system of claim 9, wherein said Si2H6 is at a concentration
of 1-10 vol % based on the overall silicon-based dopant
composition.
11. The system of claim 7, wherein a first supply vessel and a
second supply vessel are provided as part of a gas kit, said first
supply vessel comprising SiF4 and said second supply vessel
comprising Si2H6, each of said first and second supply vessel
dispensing SiF4 and Si2H6, respectively, to the ion source chamber
at controlled flow rates to produce a silicon-containing dopant
composition within the chamber comprising SiF4 and Si2H6 at a
predetermined concentration whereby the concentration of Si2H6 is
less than about 20 vol %.
12. The system of claim 11, wherein said kit comprises a first flow
controller for regulating flow of SiF4 at a first flow rate from a
first supply vessel, and said kit further comprises a second flow
controller for regulating flow of Si2H6 at a second flow rate from
a second supply vessel.
13. The system of claim 7, wherein a single supply vessel is
pre-mixed with the silicon-based dopant gas composition, further
wherein said supply vessel is a sub-atmospheric storage and
delivery vessel.
14. The system of claim 9, wherein the S2H6 is in an amount of
between 2.5 vol % to 5 vol % based on the overall volume of said
composition.
15. A method for increasing beam current during silicon ion
implantation, comprising: selecting a first silicon-based species;
selecting a second species having an ionization cross-section
higher than that of the first silicon-based species at a
predetermined operating arc voltage of an ion source to be utilized
during generation and implantation of active silicon ions;
providing the first silicon-based and the second species in one or
more supply vessels; flowing the first silicon-based species and
the second species from the one or more supply vessels into an ion
source apparatus; ionizing the first silicon-based species;
generating active silicon ions; and producing an increased beam
current in comparison to a beam current generated solely from SiF4,
wherein said increased beam current extends source life in
comparison to a beam current generated solely from SiF4.
16. The method of claim 15, wherein said second species is a
silicon-containing species, said first and second
silicon-containing species selected from the group consisting of
SiH2Cl2, Si2H6, SiH4 SiF2H2, SiF4 and any combination thereof.
17. The method of claim 15, wherein said first silicon-based
species is SiF4 and the second species is a silicon-based species
comprising Si2H6 ranging between about 2.5 vol % to about 5 vol %
based on the overall composition in the ion source apparatus.
18. The method of claim 15, wherein a first supply vessel and a
second supply vessel are provided as part of a gas kit, said first
supply vessel comprising SiF4 and said second supply vessel
comprising Si2H6, each of said first and second supply vessel
dispensing SiF4 and Si2H6, respectively, to the ion source chamber
at controlled flow rates in a co-flowed or sequentially flowed
manner to produce a silicon-containing dopant composition within
the chamber comprising SiF4 and Si2H6 at a predetermined
concentration whereby the concentration of Si2H6 is greater than
about 1 vol % and less than about 10 vol % based on a volume of the
overall composition.
19. The method of claim 15, wherein said predetermined operating
arc voltage ranges from about 80 V-120 V.
20. The method of claim 15, wherein a single supply vessel
dispenses a concentration comprising about 10 vol % or lower of
Si2H6 and the balance SiF4.
Description
RELATED APPLICATIONS
[0001] This application claims the benefit of priority to U.S.
provisional application Ser. No. 61/693,916, filed on Aug. 28,
2012, the disclosure of which is incorporated by reference herein
in its entirety.
FIELD OF INVENTION
[0002] The present invention relates to a unique combination of
silicon-containing dopant compositions, systems and methods of use
thereof for improved silicon ion implant processes, and
particularly an improved beam current.
BACKGROUND OF THE INVENTION
[0003] Ion implantation is an important process in
semiconductor/microelectronic manufacturing. The ion implantation
process is used in integrated circuit fabrication to introduce
dopant impurities into semiconductor wafers. The desired dopant
impurities are introduced into semiconductor wafers to form doped
regions at a desired depth. The dopant impurities are selected to
bond with the semiconductor wafer material to create electrical
carriers and thereby alter the electrical conductivity of the
semiconductor wafer material. The concentration of dopant
impurities introduced determines the electrical conductivity of the
doped region. Many impurity regions are necessarily created to form
transistor structures, isolation structures and other electronic
structures, which collectively function as a semiconductor
device.
[0004] The dopant impurities are generally ions derived from a
source dopant gas. An ion-source filament is used to ionize the
dopant gas source into the various dopant ionic species. The ions
produce a plasma environment within the ion chamber. The ions are
subsequently extracted from the ion chamber in the form of a
defined ion beam. The resultant ion beam is typically characterized
by a beam current. Generally speaking, a higher beam current can
allow more dopant ionic species to be available for implantation
into a given workpeice, such as a wafer. In this manner, a higher
implant dosage of the dopant ionic species can be achieved for a
given flow rate of source dopant gas. The resultant ion beam may be
transported through a mass analyzer/filter and then transported to
the surface of a workpiece, such as a semiconductor wafer. The
desired dopant ionic species of the beam penetrate the surface of
the semiconductor wafer to form a doped region of a certain depth
with desired electrical and/or physical properties.
[0005] Silicon implantation has been widely used in the
semiconductor industry for a variety of material modification
applications such as amorphization or photoresist modification. The
increasing use of Si implant steps during device fabrication is
requiring a need for an improved process for implantation of
various Si ionic dopant species characterized by an increased beam
current without compromising ion source life. The higher beam
current may allow higher equipment throughput and significant
productivity improvements. It should be understood that the terms
"Si ions", "Si ionic species", "Si ionic dopant species" and "Si+
ions" will be used interchangeably throughout the
specification.
[0006] Silicon tetrafluoride (SiF4) has been utilized as a dopant
gas source for silicon ion implantation. However, SiF4 has various
drawbacks. Of particular significance, SiF4 may be limited in its
ability to ionize and generate the requisite amount of Si+ ions to
establish the higher beam current being demanded by today's
applications. Increasing the amount of Si+ ions that are generated
from SiF4 typically requires increasing the energy inputted to the
ion source, otherwise referred to in the industry as the operating
arc voltage of the ion source. However, operating at increased
energy levels can damage the ion source components, which may
ultimately reduce the ability of the ion source to generate Si+
ions during operation. For example, as the walls of the arc chamber
increase in temperature during a typical ion implant process,
active fluorine that is released from SiF4 can more rapidly etch
and erode the tungsten chamber walls, which can cause the cathode
to be more susceptible to increased deposition of W-containing
deposits. The W-containing deposits suppress the ion source's
ability to generate the threshold number of electrons necessary to
sustain the plasma and generate Si+ ions. Additionally, more active
fluorine ions are available to propagate the so-called detrimental
"halogen cycle" by which increased chemical erosion of the ion
source chamber wall and other chamber components can occur.
Accordingly, operating the ion source chamber at higher energy
levels in an attempt to increase ionization of SiF4 has the
potential for shorter ion-source life, thereby rendering this mode
of operation undesirable.
[0007] Currently, there are no viable techniques for maintaining or
increasing the beam current of Si+ ion without damaging the ion
source chamber components. There remains an unmet need to develop
compositions, systems and methods of use thereof to improve the
beam current of the desired silicon ion species without
compromising the ion source life.
SUMMARY OF THE INVENTION
[0008] The invention relates, in part, to a composition, system and
method of use thereof for improving beam current improving silicon
ion source performance. The composition of the dopant gas utilized
has been found to have a significant impact on the ability to
improve beam current.
[0009] In a first aspect, a dopant gas composition is provided
comprising a silicon-based dopant gas composition. The composition
comprises a first silicon-based species and a second species. The
second species is selected to have an ionization cross-section
higher than that of the first silicon-based species at an operating
arc voltage of an ion source utilized during generation and
implantation of active silicon ions. The silicon-based dopant gas
composition improves the ion beam current so as to maintain or
increase beam current without degradation of said ion source in
comparison to a beam current generated from silicon tetrafluoride
(SiF4).
[0010] In a second aspect, a system for providing an improved beam
current during silicon ion implantation is provided. The system
comprises an ion source apparatus partially defined by an arc
chamber wall, wherein the chamber comprises a silicon ion source
disposed at least partially within the chamber wall. One or more
supply vessels are provided in fluid communication with said ion
source apparatus. The one or more supply vessels store
silicon-based dopant gas composition. The composition comprises a
first silicon-based species and a second species, wherein said
second species is selected to have an ionization cross-section
higher than that of the first silicon-based species at an operating
arc voltage of the ion source during implantation of active silicon
ions. One or more supply feed lines corresponding to the one or
more supply vessels. The one or more feed lines extend from the one
or more supply vessels through the wall into the chamber. The one
or more supply vessels are configured to dispense the silicon-based
dopant composition through the one or more supply feed lines and
into said ion source apparatus, thereby allowing the silicon ion
source to ionize the silicon-based dopant gas composition to
generate at least a portion of the active silicon ions from at
least said first silicon-based species. The active silicon ions
produce an increased beam current in comparison to a beam current
generated solely from SiF4.
[0011] In a third aspect, a method for increasing beam current
during silicon ion implantation is provided. The method comprises
selecting a first silicon-based species and selecting a second
species having an ionization cross-section higher than that of the
first silicon-based species at a predetermined operating arc
voltage of an ion source to be utilized during generation and
implantation of active silicon ions. The first silicon-based and
the second species are provided in one or more supply vessels. The
first silicon-based species and the second species are flowed from
the one or more of the supply vessels into an ion source apparatus.
The first silicon-based species ionizes. Active silicon ions are
generated. An increased beam current is produced in comparison to a
beam current generated solely from SiF4, wherein said increased
beam current extends source life in comparison to a beam current
generated solely from SiF4.
BRIEF DESCRIPTION OF THE DRAWINGS
[0012] The objectives and advantages of the invention will be
better understood from the following detailed description of the
preferred embodiments thereof in connection with the accompanying
figures wherein like numbers denote same features throughout and
wherein:
[0013] FIG. 1 shows an ion implanter incorporating the principles
of the invention;
[0014] FIG. 2 shows the ion implanter of FIG. 1 within a silicon
implant system;
[0015] FIG. 3 is a comparison of beam current levels of the
silicon-based dopant gas composition of the present invention with
other types of silicon-based dopant gas materials;
[0016] FIG. 4 plots the ionization cross-section for different Si
containing gases at different energy levels; and
[0017] FIG. 5 shows arc chamber deposits after operation with
different silicon-containing dopant compositions.
DETAILED DESCRIPTION OF THE INVENTION
[0018] The relationship and functioning of the various elements of
this invention are better understood by the following detailed
description. The detailed description contemplates the features,
aspects and embodiments in various permutations and combinations,
as being within the scope of the disclosure. The disclosure may
therefore be specified as comprising, consisting or consisting
essentially of, any of such combinations and permutations of these
specific features, aspects, and embodiments, or a selected one or
ones thereof.
[0019] "Si ions" as used herein and throughout the specification
means various silicon ion dopant species, including silicon or
silicon containing positive ions suitable for implantation into a
substrate.
[0020] As used herein, unless indicated otherwise, all
concentrations are expressed as volumetric percentages ("vol
%").
[0021] The present disclosure in one aspect relates to novel
silicon-containing dopant compositions, systems, and methods of use
thereof for increasing the Si beam current in comparison to
conventional silicon dopant sources. The term "silicon-based dopant
gas composition" of the present invention as used herein and
throughout the specification is intended to refer to a first
silicon based species and a second species selected such that the
second species has a higher ionization cross-section than the first
silicon based species at the selected ion implant operating
conditions (e.g., arc voltage or energy input to the ion source) as
will be described herein. "Ionization cross-section" is defined as
the probability (measured in units of area) that ionization will
occur when an atom or molecule undergoes collision with an electron
emitted from the ion source. The second species is a complimentary
gas which allows the ion source to operate at a condition that
helps maintain its efficiency for a longer duration compared to
utilizing only SiF4 in an ion implant process for silicon
implantation. The silicon-based dopant gas composition of the
present invention as will be described herein improves the
performance of ion-source in comparison to previous silicon dopant
source materials without compromising ion source life. "Ion source
performance" takes into consideration key performance metrics that
include stability of beam current, source life and the extent of
beam glitching. "Beam glitching" as used herein refers to the
voltage discharge that can result in momentary drops in the beam
current. The disclosure is set out herein in various embodiments
and with reference to various aspects and features of the
invention.
[0022] A unique silicon-based dopant gas composition enables
increased beam current relative to other conventional source dopant
gases typically utilized in silicon ion implantation without
compromising ion source life. Numerous combinations of a first
silicon-based species and a second species may be used. For
example, the first silicon-based species may include Si2H6 and the
second species may include Xe or other inert gases. In other
representative examples, SiH4 may be used with a second species
including Xe or other inerts. Alternatively, SiH2Cl2 or SiF2H2 may
be used with a second species including various diluents such as Xe
and/or Kr. In each of the examples, the second species must be
chosen so as to have a higher ionization cross-section than the
first silicon-based species along a preferred range of arc voltages
(i.e., energy input to the ion source) at which the ion source
operates so as to maintain or increase beam current without
degrading the ion source during operation of the ion source.
[0023] In a preferred embodiment, the first silicon based species
comprises SiF4, contained in a predetermined concentration at the
inlet and/or within ion source apparatus 100. In accordance with
the principles of the present invention, the SiF4 may be utilized
in combination with a second gas species that includes any suitable
inert gas or diluent gas, a second silicon-based co-species or a
combination thereof. For example, the diluent gas may include xenon
or krypton either of which is used in the ion implantation process
at a higher ionization cross-section than SiF4 at the selected
operating energy level inputted into the ion source. Other suitable
diluent or inert gases may be utilized, including Ne, He, Ar or N2,
hydrogen containing gases, or any combination thereof.
[0024] In a preferred embodiment, the first gas species is SiF4 and
the second gas species includes a second silicon-based co-species
which is added to the SiF4 in a predetermined amount. It has been
shown that adding the second silicon-based co-species in a
predetermined concentration at operating conditions of the ion
source process that causes the second Si-based co-species to have
an ionization cross-section that is higher than the SiF4 ionization
cross-section tends to increase the Si+ beam current without
requiring the need to make any additional changes in the operating
parameters. Furthermore, it has been found that at certain
preferred compositions of the silicon-containing gas mixture, it is
possible to operate the ion source at a lower arc voltage and
further reduce ion source component degradation during its
operation.
[0025] Preferably, the second silicon-based co-species comprises
disilane (Si2H6). The combination of co-species Si2H6 and SiF4 in a
specific ratio can provide the source of silicon ions available for
implantation into a given substrate. In one embodiment, the Si2H6
co-species is contained at about 1-10 vol % based on the volume of
the overall silicon-based dopant gas composition. In another
embodiment, the Si2H6 co-species is contained at about 2-7 vol %.
As will be discussed, the present invention has discovered that a
specific compositional range of Si2H6 relative to SiF4 under
selected ionization conditions of the dopant gas mixture and
operating conditions of the ion chamber enables an improvement in
beam current whereby the beam current can be increased without
degradation of the ion source. In this manner, an increased silicon
ion beam current is possible without an accumulation of deposits to
an unacceptable level that causes shortening of the source life.
Si2H6 serves as a complimentary gas when in the preferred
concentration that can allow the ion source to operate at a
condition that helps maintain its efficiency for a longer duration
compared to an ion implant process utilizing only SiF4, as will be
demonstrated in the Examples below.
[0026] Furthermore, it has been shown that adding a predetermined
amount of a second Si-based species whose ionization cross-section
is higher than the SiF4 ionization cross-section in a preferred or
optimal operating condition for SiF4 can increase the generated Si+
beam current without any need to make additional changes to the
operating parameters of the ion implantation when utilizing solely
SiF4. For example, the present invention can produce an improved
beam current (i.e., sustained or increased beam current generated
without shortened ion source life) without requiring the need for
additional energy to be inputted into the ion source when utilizing
a preferred concentration range of a mixture of SiF4 and Si2H6. In
other words, the Si2H6 is added to the SiF4 in an amount that does
not exceed an upper limit so as to increase beam current and
throughput relative to that of a beam current generated solely from
SiF4.
[0027] Furthermore, it has been found that at certain compositions
of the Si gas mixtures contemplated by the present invention, the
ion source can be operated at a lower arc voltage without a
significant reduction in beam current and which can advantageously
further reduce ion source component degradation during ion implant
operation.
[0028] In a preferred embodiment and as will be explained in the
Examples below, Si ions are implanted from a Si-containing mixture
that includes Si2H6 and SiF4 in a predetermined concentration
range. Any suitable ion implantation apparatus may be utilized with
the Si2H6 and SiF4 mixture. With reference to FIG. 1, a
representative ion implantation apparatus 100 is shown for
implanting Si ions derived from Si2H6 and SiF4. The ion source
apparatus 100 depicted in FIG. 1 has various components, including
an indirectly heated cathode (IHC) 115 which may serve as the ion
source for ionizing the silicon-based dopant gas composition of the
present invention into its corresponding silicon active ions. It
should be understood that the silicon-based dopant gas composition
is suitable with other types of ion sources known in the art,
including, for example, the Freeman sources, Bernas sources and RF
plasma sources.
[0029] The ion source apparatus 100 of FIG. 1 can be used for
producing an electron beam for implanting silicon active ions into
a semiconductor substrate. The silicon active ions are generated
from ionization of the SiF4 and Si2H6 in a manner that generates
higher Si+ beam current in comparison to a beam current generated
solely from SiF4. Without being bound by any particular theory, it
is believed that under a specific compositional range of SiF4 with
Si2H6 and carefully selected operating conditions of the ion source
apparatus 100, the SiF4 and Si2H6 interact with one another in a
synergistic manner to create an ionization mechanism that generates
an increased amount of Si+ active ions to produce an increased and
improved beam current.
[0030] FIG. 4 plots the ionization cross-section for different
silicon compounds as a function of energy. Si2H6 exhibits a higher
ionization cross-section than SiF4 at the preferred operating
energy levels or arc voltages of the ion source at which SiF4
ionization can occur. In other words, FIG. 4 shows that Si2H6 has a
higher probability of generating ions under such arc voltage
operating conditions of the ion source. The presence of ions
produced from Si2H6 augments the ionization process of SiF4
resulting in higher Si+ beam current. On the contrary, FIG. 4 shows
that SiH4 has a smaller ionization cross-section than SiF4, thus
reducing the net probability for SiF4 to interact and collide with
ionized species of SiH4 and ionize into ionized SiF4 species,
thereby resulting in a drop of Si+ beam current.
[0031] Referring to FIG. 4, Si2H6 exhibits a higher ionization
cross-section than SiF4 at the selected operating arc voltages of
about 80V-120V under which SiF4 ionization occurs. Within this
selected operating regime, Si2H6 has a higher probability of
generating various silicon-containing ions. The presence of the
silicon-containing ions derived from Si2H6 augments the ionization
process of SiF4 resulting in higher Si+ beam current without
degradation of the source filament of the ion source. However, it
has been discovered that the improvement in beam current is only
exhibited within a certain concentration range for Si2H6 that is
less than about 50%, and preferably less than about 40%, and more
preferably less than 20% and most preferably less than 10%.
[0032] As will be shown in the Examples below in connection with
FIG. 3, elevated Si2H6 concentrations of about 50% or higher of the
total gas mix caused a reduction in beam current in comparison to a
beam current produced from undiluted (i.e., pure) SiF4. Moreover,
the beam current drops significantly at 80% Si2H6 and 20% SiF4.
Under such conditions of elevated Si2H6 concentrations of about 50%
or greater, the plasma was observed to exhibit poor extraction of
the silicon ions from the arc chamber, which resulted in lower beam
current. FIG. 3 shows Si+ beam current obtained while ionizing
different Si-containing gas mixes. A Si2H6 containing gas mix (5%
Si2H6 balance SiF4) showed about a 20% increase in Si+ beam current
compared to undiluted SiF4. Furthermore, FIG. 3 shows that the
addition of other Si-containing complimentary species to SiF4
resulted in a drop of beam current. For example, as will be
discussed below in the Examples, a 50% SiF4 and 50% SiH4 gas mix
exhibited about a 5% drop in the beam current compared to a beam
current generated from undiluted SiF4 case.
[0033] Additionally, Si containing deposits were observed at these
elevated dilsilane concentrations at 50% and higher, thereby
resulting in lower beam current during the course of operation and
premature failure of the ion-source.
[0034] As a result of maintaining the Si2H6 below a predetermined
upper limit, it has been shown that the addition of a second
Si-based co-species in an amount less than SiF4 and whose
ionization cross-section is higher than the SiF4 ionization
cross-section at the preferred or optimal operating condition for
SiF4 can increase the Si+ beam current obtained without any
additional changes in the operating parameters, such as increased
arc voltage. On the contrary, the present invention has
surprisingly found that at certain compositions of Si2H6 and SiF4,
the ion source can actually be operated at a lower arc voltage that
is capable of maintaining substantially the same beam current while
prolonging source life (i.e., ion source component degradation as a
result of cathode thinning and/or fluorine attack is avoided). The
ability to operate at a reduced arc voltage and still maintain
substantially the same beam current is possible as a result of the
corresponding ionization cross-sectional curves of Si2H6 and SiF4
shown in FIG. 4. For example, a reduction in arc voltage from about
110 V to about 80 V can occur due to the increasing difference
between the ionization cross-sectional curves of Si2H6 and the SiF4
at the lower arc voltages, as shown in FIG. 4. A larger difference
in ionization cross-sectional difference between Si2H6 and SiF4 is
seen to occur at relatively lower arc voltages, which can allow a
higher likelihood that a sufficient number of Si active ions will
be generated to offset any tendency for a decrease in overall beam
current due to less arc voltage. In other words, although the lower
arc voltage may potentially result in a lower amount of Si total
ions that are generated, the increased ionization cross-sectional
difference enables sufficient ionization to maintain beam current
while significantly reducing fluorine attack and cathode thinning,
thereby extending ion source life and ultimately improving
throughput. Selection of an optimal operating voltage (i.e., energy
input to the ion source) is a function of the gas species and their
corresponding ionization cross-sectional curves. The optimal arc
voltage will allow maintenance or increase of beam current without
degradation of the ion source. In one embodiment, optimal voltage
occurs in a range between 85-95 V.
[0035] Additionally the dopant gas composition disclosed in this
invention preferably allows the ion source cathode 115 life to be
extended compared to conventional silicon dopant ion implantation
systems, at least in part, on the basis of minimal rate of weight
change of the source cathode 115 during the operation of the ion
source apparatus 100. The net result is an ion source cathode 115
that is not subject to premature failure, thereby allowing the
source cathode 115 to remain operational for an extended period of
time to increase throughput. In this manner, the present invention
possesses a unique silicon-based dopant gas composition capable of
maintaining or increasing silicon ion beam current relative to a
beam current generated solely from SiF4 while simultaneously
maintaining the integrity of the source filament 115 for a longer
duration than previously possible utilizing conventional silicon
precursor materials such as SiF4.
[0036] Still referring to the ion source apparatus 100 of FIG. 1, a
silicon dopant gas composition stream 102 comprising SiF4 and Si2H6
in a predetermined ratio is introduced into an ion source chamber
112 through a gas feed line extending through arc chamber wall 111.
In one embodiment, the Si2H6 is maintained below 50% based on the
overall composition stream 102. In another embodiment, the Si2H6 is
maintained at a concentration between 1-20%. In yet another
embodiment, the Si2H6 is at or below about 10%. The silicon dopant
gas composition 103 inside the source chamber 112 is subject to
ionization by applying a predetermined voltage from a power supply
source (not shown) to resistively heat a tungsten-based filament
114 positioned in close proximity to the IHC 115. The filament 114
may be negatively biased relative to the IHC 115. A current is
applied to the filament 114 through the power supply source to
resistively heat the filament 114. An insulator 118 is provided to
electrically isolate the cathode 115 from the arc chamber wall
111.
[0037] Electrons are emitted by the cathode 115. The emitted
electrons accelerate and ionize the SiF4 and Si2H6 of the silicon
dopant composition 103 molecules to produce a plasma environment
within the chamber 112. The repeller electrode 116 builds up a
negative charge to repel the electrons back to sustain ionization
of silicon dopant composition 103 molecules, thereby maintaining
the plasma environment in the arc chamber 112. Repeller electrodes
116 are preferably configured substantially diametrically opposed
to the IHC 115 to maintain ionization of the dopant gas composition
103 within the chamber 112. The arc chamber wall 111 includes an
extraction aperture 117 through which a well defined silicon ion
beam 121 is extracted from out of the arc chamber 112. The
extraction system includes extraction electrode 120 and suppression
electrode 119 positioned in front of the extraction aperture 117.
Both the extraction and suppression electrodes 120 and 119 have
respective apertures aligned with the extraction aperture 117 for
extraction of the well-defined ion beam 121 that can be used for
silicon ion implantation.
[0038] Ionization of the silicon-based dopant gas composition 103
may cause generation of a variety of ionized species from a
synergistic interaction of the SiF4 with Si2H6, including F ions,
silicon-fluoride ions and various silicon-containing ions to be
released from co-species SiF4, and hydrogen, silicon-hydride and
additional silicon-containing ions to be released from co-species
Si2H6. A large amount of the released F ions are available for
scavenging by hydrogen. Additionally, the released F ions can
recombine with some of the gaseous silicon ions formed from
ionization of the dopant gas mixture. However, under sufficient
operating conditions, including selection of an arc voltage that
favorably allows synergistic interaction of Si2H6 with SiF4 within
ion source apparatus 100 by virtue of their corresponding
ionization cross-sections at the selected operating arc voltage
(FIG. 4) and by controlling the relative amounts of SiF4 and Si2H6
introduced into the ion chamber in accordance with principles of
the present invention, the amount of silicon ions which recombine
with F ions is substantially minimized so as to generate a maximal
concentration level of active silicon ion available for ion
implantation that increases beam current. As a result, the manner
in which F ions are scavenged makes available less F ions to etch
W-based chamber components from ion source apparatus 100 and form
W-containing deposits, while maintaining a sufficient amount of
active silicon ions for implantation. Reducing the formation of
W-containing deposits translates into less diffusion and
decomposition of W-containing deposits onto the hotter surfaces of
IHC 115. Accordingly, the rate of weight gain of the IHC 115 during
operation of the ion source apparatus 100 is substantially reduced.
The end result is a lower frequency or elimination of beam
glitching, thereby increasing beam stability and extending the
operational lifetime of the ion source apparatus 100.
[0039] The scavenging of the F ions by virtue of the interaction of
the SiF4 and Si2H6 co-species can help, at least in part, create an
enhanced ionization mechanism which generates increased amounts of
active silicon ions that are greater than the simple additive
effect of total Si ions that would be available by individually
ionizing SiF4 and Si2H6. Furthermore, the SiF4 and Si2H6 co-species
in combination may be interacting in a favorable manner as
explained in terms of their ionization cross-sections that improves
their respective ionization characteristics. While the specific
ionization mechanism is not fully understood, the overall effect of
the release of silicon ions is a synergism that yields an improved
and sustained beam current which does not incur momentary drops in
current, as typically observed by silicon dopant gases used with or
without a diluent gas. The active concentration of silicon ions
available for ion implantation is maintained at sufficient levels
at least in part because the present invention utilizes two silicon
co-species in a specific ratio from which silicon ions are derived.
Further, accumulation of deposits are avoided or substantially
minimized, thereby eliminating the need for incorporating a
diluents or inert gas. The improved and sustained beam current of
the present invention translates into higher throughput and
productivity, in which required silicon ion dosage implanted into
the substrate can be achieved in a shorter time period.
[0040] In this manner, unlike the prior art, the present invention
utilizes a dual purpose silicon dopant gas composition, such as
SiF4 and Si2H6 in a preferred concentration, and under carefully
selected ionization conditions and energy inputted into the
tungsten-based filament 114 which can increase silicon beam current
without compromising ion source life. The SiF4 and Si2H6 interact
with one another in a synergistic manner to create an ionization
mechanism that generates an increased amount of Si+ ions at least
in part by virtue of the higher ionization cross-section
complementary gas species Si2H6 exhibits over SiF4 within the
selected operating range of 80V-120V and furthermore because the
concentration of Si2H6 is maintained below a predetermined upper
limit of 50% or less.
[0041] FIG. 2 shows the ion source apparatus 100 of FIG. 1
incorporated into a silicon ion implant system 200. It should be
appreciated by one skilled in the art that that all of the elements
of the ion source apparatus 100 of FIG. 1 are incorporated into
FIG. 2. As a result, the elements and features of the ion source
apparatus 100 shown in FIG. 2 should be understood in relation to
the elements and features shown in FIG. 1.
[0042] FIG. 2 shows that the silicon-based dopant gas composition
can be supplied form a dopant gas box 201. The silicon-based dopant
gas composition can be provided as a pre-mixed composition in a
single supply vessel within gas box 201 at the desired formulation.
Alternatively, the gas box 201 may be constructed and arranged such
that each of the silicon co-species, SiF4 and Si2H6, can be
supplied in separate dispensing vessels as part of a gas kit which
are then co-flowed or sequentially flowed, continuously or
semi-continuously, at controlled flow rates utilizing corresponding
flow controllers which may be considered part of the gas kit. The
flow rates of Si2H6 and SiF4 are controlled and directed towards
the ion source apparatus 100 to create the desired silicon-based
dopant gas composition at the preferred concentration ranges. Such
dopant gas composition can produced at either the inlet to the
source chamber 100 and/or therewithin. The point at which the
individual co-species converge can occur upstream of the ion source
apparatus 100 or within the chamber 112 of the apparatus 100.
[0043] Still referring to FIG. 2, a suitable analyzer as
commercially available and known in the art can be used to measure
the concentration of the silicon-based dopant gas composition
entering the ion source chamber 100. In one embodiment, the silicon
dopant gas composition has a concentration that ranges between
about 1-20 vol % Si2H6 with the balance SiF4. In a preferred
embodiment, the silicon dopant gas composition has a concentration
that ranges between about 2-10 vol % Si2H6 with the balance SiF4.
In a more preferred embodiment, the silicon dopant gas composition
has a concentration that ranges between about 2-5 vol % Si2H6 with
the balance SiF4.
[0044] Still referring to FIG. 2, the silicon-based dopant gas
composition is introduced from box 201 into the ion source
apparatus 100 as a pre-mixed single source or as individual species
of SiF4 and Si2H6 in the manner immediately described above in
either a co-flown or sequentially flowed manner into the apparatus
100. A voltage is applied to ion source filament 114 as a means for
introducing energy into the chamber 112 (FIG. 1) to generate the
selected arc voltage of apparatus 100 to ionize the silicon-based
dopant gas composition and produce a sufficient concentration of
active silicon ions available for implantation. Preferably, the
energy inputted to the ion source 114 (i.e., arc voltage) is
maintained in a range of about 80V-120V so as to enable interaction
of SiF4 and Si2H6 in a synergistic manner to create an ionization
mechanism that generates an increased amount of active Si+ ions. A
resultant plasma environment within the chamber 112 is produced.
The ion beam extraction system 201 includes extraction electrode
120 and suppression electrode 119 that form part of the
silicon-containing dopant supply system as shown in FIG. 2 and
which are configured for extraction of a well-defined silicon beam
121 to be used for silicon ion implantation. The beam 121 may be
transported through an optional mass analyzer/filter 205 to select
and magnetically capture the silicon ion species from other species
to be implanted. Specifically, the mass analyzer/filter 205 is
arranged to permit only the targeted active silicon ions to travel
onwards into the process chamber or end station 210. The
silicon-rich ion beam 207 can then be accelerated/decelerated by
acceleration/deceleration unit 206 as required and then transported
to the surface of a wafer or target workpiece 209 positioned in an
end station 210 for implantation of the active silicon ions into
the workpiece 209. The active silicon ions of the beam collide with
and penetrate into the surface of the workpiece 209 at the desired
depth to form a region with the desired electrical and physical
properties. By employing the process and techniques of this
invention, the beam current of the ion source apparatus 100
included within system 200 can be significantly increased over
conventional silicon dopant systems without incurring a drop in ion
source life. As such, the present invention represents an
advancement in the silicon ion implantation industry which, among
other process benefits, increases throughput of the ion source
apparatus 100.
[0045] It should be noted many variations in the structure and
design of the silicon implant process 200 may be employed in
different embodiments of the present invention. Furthermore, the
details of the construction and design are not important in the
performance of the present invention, except insofar as they relate
to the silicon-based dopant composition used in the ion source
apparatus 100 and corresponding implant process 200.
[0046] In a preferred aspect of the invention shown in FIG. 2, a
controlled flow of the silicon-based dopant gas composition
comprising Si2H6 and SiF4 is supplied pre-mixed to the ion source
chamber 112 of the ion source apparatus 100 in which the
concentration of the Si2H6 ranges from about 1-10 vol % based on
the overall mixture. The silicon-based dopant gas composition can
be packaged pre-mixed in a high pressure cylinder. Alternatively,
the dopant gas composition may be delivered from a sub-atmospheric
delivery package such as, by way of example, an UpTime.RTM.
sub-atmospheric delivery system as disclosed in U.S. Pat. Nos.
5,937,895; 6,045,115; 6,007,609; 7,708,028; and 7,905,247, all of
which are incorporated herein by reference in their entirety. Other
suitable sub-atmospheric delivery devices may include pressure
regulators, check valves, excess flow valves and restrictive flow
orifices in various arrangements. For example, two pressure
regulators may be disposed in series within the cylinder to down
regulate the cylinder pressure of the dopant gas to a predetermined
pressure acceptable for downstream mass flow controllers contained
along the fluid discharge line. A sub-atmospheric package is a
preferred mode for delivery of the gas due to its enhanced safety.
In one embodiment, the flow rate of can range from about 0.1-100
sccm, preferably 0.5-50 sccm and more preferably from about 1-10
sccm. The ion source apparatus 100 can include any of the commonly
used ion sources in commercial ion implanters, such as Freeman and
Bernas type sources, indirectly heated cathode sources and RF
plasma sources. The ion source operating parameters including
pressure, filament current and arc voltage, are tuned to achieve
desired ionization of the silicon-based dopant gas composition
comprising Si2H6 and SiF4 such that under the selected parameters,
the Si2H6 possesses a higher ionization cross-section compared to
SiF4 thereby enhancing ionization and generation of active Si ions
in accordance with principles of the present invention.
[0047] In another embodiment of the present invention, the
Si-containing dopant composition is a mixture of SiF4 and Si2H6 at
the prescribed concentrations discussed above that may be operated
at a lower arc voltage for suitable ion implant applications. The
lower voltage may reduce the attack on chamber components. In
particular, operating at a lower arc voltage results in less
chemical as well as physical erosion of the components, thereby
extending the lifetime of the ion-source. Operating at a lower arc
voltage preferably results in substantial maintenance of beam
current. Advantageously, the reduction in arc voltage does not
result in accumulation of deposits and beam instability, as is the
case with a beam generated solely from undiluted SiF4 in which
accumulation of W-containing deposits on the filament reduces the
electron emission efficiency of the ion source, which can
potentially result in a loss of beam current due to insufficient
ionization of the source gas.
[0048] Applicants have performed several experiments to compare the
silicon-based dopant gas compositions of the present invention with
other dopant gas materials, as will now be discussed in the
Examples below. It should be noted that for all tests described
below, the ion source filament weight gain or loss was measured by
taking weight measurements of the ion source filament before and
after the test as known in the art. The current was measured using
a Faraday cup by standardized techniques well known in the art. All
tests were run at 100V.
Comparative Example 1
Undiluted SiF4
[0049] An ionization test was performed to evaluate ion beam
performance of an ion beam derived from a dopant gas composition of
SiF4 only (i.e., undiluted). The interior of the chamber consisted
of an ion source that was constructed to include a helical filament
and anode situated perpendicular to an axis of the helical
filament. A substrate plate was positioned in front of the anode to
keep the anode stationary during the ionization process. The SiF4
was introduced into the ion source chamber. Voltage was applied to
the ion source to ionize the SiF4 and produce silicon ions. The
beam current that was measured is shown in FIG. 3. The beam current
was considered acceptable for purposes of generating a well-defined
silicon ion beam that could be used for ion implantation. However,
a significant filament weight gain of 0.02 gm/hr was observed and
determined as shown in Table 1. The accumulation of various
W-containing deposits on the filament during the test reduced its
electron emission efficiency resulting in eventual loss of beam
current due to insufficient ionization of the source gas, which
required the test to be aborted. These results were believed to be
typical of problems encountered with utilizing solely SiF4 as the
Si+ dopant source.
Comparative Example 2
SiF4+20% Xe/H2
[0050] An ionization test was performed to evaluate the ion beam
current obtained from a silicon-based dopant gas composition
composed of a mixture of SiF4 and a diluent gas mixture of
xenon/hydrogen at 20 vol % of the total gas mix, along with the
performance of the ion-source during the course of ionization for a
certain duration. The same ion source chamber was utilized as when
performing the baseline SiF4 test in Comparative Example 1. The
SiF4 and diluent xenon/hydrogen were introduced from separate
sources into the ion source chamber to produce the desired dopant
gas composition within the chamber. Voltage was applied to the ion
source to ionize the SiF4 and produce silicon ions. Beam current
was measured and determined to be about 10% lower than that
produced with utilizing only SiF4, as shown in FIG. 3 at Case B.
Beam current was normalized against that of SiF4 from Comparative
Example 1 and is shown in FIG. 3. A weight gain of 0.0017 gm/hr of
the filament was obtained as shown in Table 1. Weight gain of the
filament due to deposits was less than that of SiF4 from
Comparative Example 1, indicating less active F ions were available
to sustain the halogen cycle and therefore etch additional tungsten
chamber components. As a result, the halogen cycle was reduced
relative to that of Comparative Example 1. Less beam glitching
occurred relative to Comparative Example 1. However, the
xenon/hydrogen diluent reduced the halogen cycle and W-containing
deposits at the expense of generating a beam current lower than
that of utilizing solely SiF4 (FIG. 3). These results were
indicative of conventional silicon dopant gas precursors that use a
diluent gas.
Comparative Example 3
50% SiF4+50% SiH4
[0051] An ionization test was performed to evaluate the ion beam
current obtained from a silicon-based dopant gas composition
composed of a mixture of SiF4 and SiH4, along with the performance
of the ion-source during the course of ionization for a certain
duration. The concentration of the mix was 50 vol % SiF4 and 50 vol
% SiH4. The same ion source chamber was utilized as when performing
the tests in Comparative Examples 1 and 2. The SiF4 and SiH4
mixture was introduced from separate sources into the ion source
chamber to produce the desired dopant gas composition within the
chamber. A concentration measurement was obtained to confirm the
target concentration was achieved. Voltage was applied to the ion
source to ionize the dopant gas mixture and produce silicon ions.
Beam current was measured and normalized against that of SiF4, as
shown in FIG. 3 at Case C. The beam current was determined to be
higher than that produced when utilizing the SiF4 and diluent
xenon/hydrogen mixture of Comparative Example 2, but lower than
that produced when utilizing only SiF4 of Comparative Example 1.
The results may be explained, at least in part, by reference to
FIG. 4, which shows that SiH4 has a lower ionization constant than
that of SiF4 at virtually all operating energy levels inputted to
the ion source. As such, less active silicon ions derived from
collision of SiH4 and SiF4 were generated. Because SiH4 has a
smaller ionization cross-section than SiF4, there may been a
reduction in the net probability of SiF4 to undergo collision and
ionize, thereby resulting in an overall drop of silicon ion beam
current. A weight loss of 0.0025 gm/hr of the filament was obtained
as shown in Table 1. Thinning of the filament was observed as a
result of possible physical sputtering of the filament by
corresponding positive ionic species of SiF4 and SiH4 within the
ion chamber. It was therefore concluded that a 50% SiF4 and 50% vol
% SiH4 dopant gas mixture could result in premature failure due to
excessive ion source filament thinning.
Comparative Example 4
SiF4+50% Si2H6
[0052] An ionization test was performed to evaluate the ion beam
current obtained from a silicon-based dopant gas composition
composed of SiF4 and 50 vol % Si2H6, along with the performance of
the ion-source during the course of ionization for a certain
duration. The same ion source chamber was utilized as when
performing the tests in Comparative Examples 1, 2, 3. The
silicon-based dopant gas composition was introduced into the
chamber via separate SiF4 and Si2H6 sources and mixed in the flow
lines upstream of the ion source chamber. A concentration
measurement was obtained to confirm the target concentration was
achieved. Voltage was applied to the ion source to ionize the
dopant gas composition and produce silicon ions. Beam current was
measured and normalized against that of SiF4. FIG. 3 at Case F
shows that the beam current obtained was about 10% lower than SiF4
(Comparative Example 1). The filament lost weight at a rate of
0.0023 gm/hr. Significant Si containing deposits were observed
along surfaces of the ion source arc chamber after continued
operation for 20 hrs, as shown in FIG. 5B. Such accumulation of
deposits resulted in beam instability during the course of
operation and eventual pre-mature failure of the ion source. Hence,
it was concluded that this gas composition was undesirable for Si
implant operation.
Comparative Example 5
SiF4+80% Si2H6
[0053] An ionization test was performed to evaluate the ion beam
current obtained from a silicon-based dopant gas composition
composed of SiF4 and 80 vol % Si2H6, along with the performance of
the ion-source during the course of ionization for a certain
duration. The silicon-based dopant gas composition was introduced
into the chamber via separate SiF4 and Si2H6 sources and mixed in
the flow lines upstream of the ion source chamber. The same ion
source chamber was utilized as when performing the tests in
Comparative Examples 1, 2, 3 and 4. The pre-mixed silicon-based
dopant gas composition was introduced into the chamber. A
concentration measurement was obtained to confirm the target
concentration was attained. Voltage was applied to the ion source
to ionize the dopant gas composition and produce silicon ions. Beam
current was measured and normalized against that of SiF4. The
mixture of 80% Si2H6 balance SiF4 exhibited a significantly lower
measured Si+ beam current compared to the undiluted SiF4 baseline
case of Comparative Example 1. FIG. 3 at Case G shows that the beam
current was more than 60% lower than SiF4 (Comparative Example 1).
Furthermore, the ion beam exhibited instability during the course
of operation and eventually resulted in pre-mature failure of the
ion source. The filament lost weight at a rate of -0.0025 gm/hr as
shown below in Table 1. FIG. 5A shows that undesirable amounts of
Si-containing deposits along surfaces of the arc chamber were
observed after continued operation for 20 hrs. Hence, it was
concluded that this Si-containing dopant gas composition was
undesirable for Si ion implant operation.
Example 1
SiF4+2.5 vol % Si2H6
[0054] An ionization test was performed to evaluate the ion beam
current obtained from a silicon-based dopant gas composition
composed of SiF4 and 2.5 vol % Si2H6, along with the performance of
the ion-source during the course of ionization for a certain
duration. The same ion source chamber was utilized as when
performing the tests in Comparative Examples 1, 2, 3, 4 and 5. The
silicon-based dopant gas composition was produced by co-flowing
into the chamber a 5% Si2H6/SiF4 mix and a pure SiF4 stream at
selected flow rates such that the pure SiF4 stream diluted the 5%
Si2H6/SiF4 mix to produce 2.5 vol % Si2H6. A concentration
measurement was taken to confirm the target 2.5 vol % Si2H6 was
produced. Voltage was applied to the ion source to ionize the
silicon-based dopant gas composition and produce silicon ions. Beam
current was measured and normalized against that of SiF4. Beam
current as shown in FIG. 3 at Case E was determined to be higher
than that produced when utilizing the SiF4. A weight loss of
-0.0009 gm/hr of the filament was obtained as shown in Table 1. The
silicon-based dopant composition produced the least amount of
weight change of the filament of all tests. Furthermore, FIG. 5C
shows virtually no deposits were observed along the surfaces of the
arc chamber. It was therefore concluded that the SiF4 and 2.5 vol %
Si2H6 dopant gas composition can produce higher beam currents than
SiF4 while significantly reducing W-based deposits on the source
filament as well as avoiding physical sputtering of the
filament.
Example 2
SiF4+5 vol % Si2H6
[0055] An ionization test was performed to evaluate the ion beam
current obtained from a silicon-based dopant gas composition
composed of SiF4 and 5 vol % Si2H6, along with the performance of
the ion-source during the course of ionization for a certain
duration. The same ion source chamber was utilized as when
performing the tests in Comparative Examples 1, 2, 3 and Example 1.
The silicon-based dopant gas composition was introduced from
separate sources and pre-mixed upstream of the chamber. A
concentration measurement was taken to confirm the target 5 vol %
Si2H6 was produced. Voltage was applied to the ion source to ionize
the dopant gas composition and produce silicon ions. Beam current
was measured and normalized against that of SiF4. Beam current as
shown in FIG. 3 at Case D was determined to be highest amongst all
tested dopant gas compositions. No premature beam glitching
occurred as a result of filament weight gain or erosion. A weight
loss of -0.0012 gm/hr of the filament was obtained as shown in
Table 1. The weight change of the filament was less than that of
all of the Comparative Examples 1-3 and comparable to that of
Example 1. No deposits were observed during the test. Although the
weight decrease was slightly more than that of SiF4+2.5 vol % Si2H6
in Example 1, the weight decrease did not produce beam instability.
It was therefore concluded that the SiF4 and 5 vol % Si2H6 dopant
gas composition could produce higher beam currents than that
utilizing solely SiF4 while significantly reducing W-based deposits
and physical sputtering on the source filament.
TABLE-US-00001 TABLE 1 Source life evaluation Filament Si
containing Dopant Gas weight deposits in Composition gain/loss rate
arc chamber SiF.sub.4 only +0.02 gm/hr No SiF.sub.4 + Xe/H.sub.2
+0.0017 gm/hr No SiF.sub.4 + SiH.sub.4 -0.0025 gm/hr No SiF.sub.4 +
Si.sub.2H.sub.6 -0.0009 gm/hr No (2.5%) SiF.sub.4 + Si.sub.2H.sub.6
-0.0012 gm/hr No (5%) SiF4 + Si2H6 -0.0023 gm/hr Yes (50%) SiF4 +
Si2H6 -0.0025 gm/hr Yes (80%)
[0056] The Examples demonstrate that an upper limit exists on the
Si2H6 concentration in a mixture of Si2H6-SiF4 to realize the
benefits of a dopant gas composition disclosed in the present
invention. FIGS. 5A-5C show the interior of an arc chamber after
continuous operation with different concentrations of Si2H6 in a
mixture of SiF4 and Si2H6. The composition with 80% and 50% Si2H6,
respectively, each exhibited undesirable amounts of deposits in the
arc chamber after continued operation for 20 hrs whereas no
deposits were observed for 2.5% Si2H6-SiF4 mix even after 60 hours
of continued operation. Additionally, it was discovered that at
higher Si2H6 compositions of 50% and 80%, the ionization process
results in Si and/or W containing deposits inside the arc chamber.
Such deposits are undesirable and lower the active Si ions which
leads to a reduction in Si+ beam current during the course of
operation. As a result, subsequent premature failure of the ion
source can occur. These observations place an upper limit on the
preferred composition for a Si2H6-SiF4 mix to realize the benefits
of improved beam current characterized by increased beam current
without ion source degradation during operation.
[0057] The invention further demonstrates that the etching of
W-containing and other various types deposits from chamber wall
components is significantly reduced when using the silicon-based
dopant gas composition of the present invention. Reduction of
deposits reduces or eliminates beam instability and eventual beam
glitching, thereby improving the beam current during source life of
the ion chamber. Furthermore, unlike prior art methods, the
compositions, systems and methods of use for this invention can
increase the beam current without compromising and shortening the
ion source life. Surprisingly, as shown in FIG. 3, increased beam
current can be achieved compared to undiluted SiF.sub.4. The
ability to increase the number of Si dopant active ions per unit
volume of gas flow as compared to undiluted or pure SiF4 increases
the Si beam current for the same amount of gas flow without
degradation of the ion source. Increased beam current coupled with
extended ion source can increase throughput and provides an
opportunity for reducing cycle time to achieve the required dopant
dosage of the process workpieces.
[0058] From an ionization standpoint, Examples 1 and 2 also
demonstrate that specific silicon-containing compositions of the
present invention can generate active ions and an increased beam
current without degradation of the ion source. In particular, a
Si2H6 and SiF4 mixture within preferred concentration ranges at
selected arc voltage operating conditions facilitate interaction
with one another in a synergistic manner to create an ionization
mechanism which can generate an increased amount of active silicon
ions that is greater than the simple additive effect of total
silicon ions that would be available from individually ionizing SF4
and Si2H6. The net effect is an improvement in beam current in
comparison to conventional systems and processes employing
conventional silicon precursor materials.
[0059] Additionally, the present invention can overcome the
drawbacks of conventional silicon ion implant systems and methods
which require a diluent gas for the purpose of reducing deposits.
Diluent gases tend to reduce the active number of silicon ions
available per unit gas flow into the ion source chamber, thereby
reducing throughput. Accordingly, this so-called "dilution effect"
typically encountered with conventional silicon dopant compositions
employing a dopant gas with diluent gas resulting in lower silicon
ion beam current is eliminated in the present invention. The
present invention does not rely on incorporation of a diluent gas
for purposes of extending source life. However, the present
invention does contemplate in specific instances the incorporation
of a diluent or inert gas as a second species in a specific manner
whereby it has a higher ionization cross section than a first
silicon-containing species. In this manner, the present invention
possesses a unique silicon-based dopant gas composition, system and
method of use thereof capable of maintaining or increasing silicon
ion beam current while simultaneously maintaining the integrity of
the source filament 115 for a longer duration than previously
possible utilizing conventional silicon precursor materials.
[0060] The present invention also offers other process benefits.
For example, the increased beam current attainable in the present
invention can eliminate the requirement of any additional gas stick
(e.g., flow control device, pressure monitoring device, valves and
electronic interface), and therefore offers a significant reduction
in capital expense associated with utilizing additional gas
sticks.
[0061] While it has been shown and described what is considered to
be certain embodiments of the invention, it will, of course, be
understood that various modifications and changes in form or detail
can readily be made without departing from the spirit and scope of
the invention. It is, therefore, intended that this invention not
be limited to the exact form and detail herein shown and described,
nor to anything less than the whole of the invention herein
disclosed and hereinafter claimed.
* * * * *